Current semiconductor technology typically involves incorporating dopant material in various portions of a semiconductor device including, for example, the substrate of the device or a layer formed over the substrate. One typical example of a semiconductor device is a metal-oxide-semiconductor (MOS) transistor. The principal elements of a typical MOS semiconductor device are illustrated in FIG. 1. The device generally includes a semiconductor substrate 101 on which a gate electrode 103 is disposed. The gate electrode 103 acts as a conductor and is typically formed of polysilicon with a dopant material at a desired concentration.
Source/drain regions 105 are formed in the semiconductor substrate 101 adjacent to the gate electrode 103. Generally, the source/drain regions 1 05 are formed by implanting a dopant material into the substrate. Following the dopant implant, the substrate is typically annealed to drive the dopant material deeper into the substrate 101 and to more uniformly dope the source/drain regions 105. The thickness of each source/drain region 105 is generally a function of the dopant concentration and the amount of annealing.
A channel region 107 is formed in the semiconductor substrate 101 beneath the gate electrode 103 and separates the source/drain regions 105. The channel is typically lightly doped with a dopant material of a type opposite that of the source/drain regions 105. The gate electrode 103 is generally separated from the semiconductor substrate 101 by an insulating layer 109, for example an oxide layer such as SiO.sub.2.
One commonly used substrate material is silicon. Dopant materials for use with silicon are often electron donors or acceptors (or, alternatively, hole acceptors and donors), such as Group III and Group V elements including, for example, boron, nitrogen, arsenic, and phosphorus. The operational parameters of a particular semiconductor device often depend, at least in part, on the concentration and depth profile of the dopant material. In some cases, the allowed tolerances in the variation in dopant concentration may be very narrow. Therefore, it is desirable to have methods to determine the dopant concentration and profile in a semiconductor device.
Determination of the concentration and profile of a dopant material in a region of a semiconductor device, such as the gate electrode, source/drain regions, or channel region can be done in several ways. One method includes measuring particular electrical properties of a region of the semiconductor device which may be characteristic of the presence of the dopant material or characteristic of damage caused by the incorporation of the dopant material in the semiconductor by methods such as ion implantation. Many of these electrical property measurement techniques, however, are limited to the determination of the concentration of the dopant material. Those which are used to determine the profile of the dopant in the semiconductor are typically destructive and invasive. For example, depth profile measurement techniques may include measuring the electrical properties of a doped region, removing a portion of the doped region, and remeasuring the electrical properties of the region. The measurements are typically obtained at intervals as increasing amounts of the doped region are removed to provide a depth profile of the region.
Another conventional method for determining the concentration and, more particularly, the depth profile of the dopant material is secondary ion mass spectroscopy (SIMS). This method involves bombarding the surface of a semiconductor region with an ion beam which causes the ejection of material from the semiconductor surface. The mass of the ejected material is measured by a mass spectrometer to determine the composition of the semiconductor device. A profile of dopant concentration can be obtained by observing the ejected material over time. This method is also invasive and destructive.
One noninvasive method is Nuclear Depth Profiling (NDP) which requires that the semiconductor device be bombarded by energetic neutrons from a source, such as a nuclear reactor. The neutrons bombard the semiconductor device and cause the ejection of measurable particles as the neutrons encounter a dopant material like boron. This method, however, cannot be used on the fabrication line because it requires a source of energetic neutrons.